Gypsum plaster-based material containing an EDTA metal complex

ABSTRACT

A plaster-based material, in particular a plasterboard intended for the interior fitting of dwellings, contains a metal complex of EDTA. The plaster-based material is used for reducing the amount of volatile organic compounds present in the atmosphere inside dwellings, offices or public buildings.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage of International ApplicationNo. PCT/FR2014/053525, filed Dec. 23, 2014, which in turn claimspriority to French Application No. 1450027, filed Jan. 3, 2014. Thecontents of all of these applications are incorporated herein byreference in their entirety.

The invention relates to a plaster-based material that is capable ofreducing the amount of volatile organic compounds in the ambient air, inparticular a plasterboard intended for the interior fitting ofdwellings.

Very diverse composite materials are used in the field of constructionand of fitment of buildings in general, especially dwellings or officesor public buildings (museums, cinemas, concert halls, etc.). Some ofthese materials such as sound and/or heat insulators, wood panels, anddecorative and furniture elements, use adhesives, paints and varnishesbased on resins that contain or release over time volatile organiccompounds. These compounds are found in the ambient air and, althoughthe amount thereof appears low they may in the long run trouble or evenimpair the health of individuals exposed thereto.

In recent years, the proportion of volatile organic compounds in theabovementioned resins has greatly increased due to stricter regulations.However, attempts to replace these resins with others free of volatileorganic compounds have been unfruitful since the proposed replacementresins are more expensive and the products obtained have lowerperformance qualities.

The aim of the present invention is to reduce the content of volatileorganic compounds inside buildings, in particular buildings for use asdwellings or offices and public buildings, so as to improve the qualityof the ambient air. The targeted volatile organic compounds are moreparticularly aldehydes, ketones and aromatic compounds.

To achieve this aim, the present invention proposes a plaster-basedmaterial, especially a plasterboard, containing a metal complex ofethylenediaminetetraacetic acid (referred to hereinbelow as the “metalcomplex of EDTA”).

Another subject of the invention concerns the use of the saidplaster-based material for reducing the amount of volatile organiccompounds in the interior air of buildings, in particular aldehydes,ketones and aromatic compounds.

In the present patent application, the term “volatile organic compound”denotes a compound containing carbon and at least one of the followingelements: hydrogen, halogen, oxygen, sulfur, phosphorus, silicon andnitrogen, with the exception of carbon oxides and mineral carbonates andbicarbonates, which have a vapour pressure at least equal to 0.01 kPa ata temperature of 293.15 K. The volatile organic compounds that are mostparticularly targeted by the present invention are compounds containingcarbon, hydrogen and oxygen, especially aromatic compounds and ketones.

In the metal complex of EDTA in accordance with the invention, the metalis preferably chosen from sodium, potassium, calcium, cerium, iron,copper and zinc, and advantageously zinc.

The total amount of metal complex of EDTA to be used generally rangesfrom 0.0001 to 40 parts by weight per 100 parts by weight of plaster,preferably from 0.001 to 10 parts and advantageously from 0.05 to 5parts.

The plaster-based material may also contain additives that improve thephysicochemical properties of the final product and afford goodmanufacturing and application conditions. The said material may thuscomprise the following additives in the following weight proportions,expressed per 100 parts by weight of plaster:

-   -   0.1 to 15 parts of an adhesion agent whose function is to        increase the adhesion of the paper coating to the plaster, for        example a starch, especially pretreated with an acid, a dextrin        or a vegetable flour, especially wheat or corn flour,    -   0.001 to 10 parts of a setting accelerator, for example hydrated        calcium sulfate or potassium sulfate,    -   0 to 10 parts of a biocide, for example sodium omadine,    -   0.0001 to 1 part of a foaming agent whose role is to create        pores so as to reduce the density of the final product, in        particular of plasterboards. An example that may be mentioned is        sodium lauryl sulfate,    -   0 to 10 parts of at least one water repellent, for example a        siloxane or a polysiloxane,    -   0 to 20 parts of at least one fire retardant, for example        vermiculite, silica, especially of micrometric size, a clay or        metal fibres,    -   0 to 20 parts of at least one reinforcer, for example polymer        fibres, mineral fibres, especially glass fibres, and animal or        vegetable fibres,    -   0 to 20 parts of an agent capable of trapping formaldehyde, for        example acetoacetamide, adipic acid dihydrazide and a protein,        and    -   0 to 20 parts of a material having a high specific surface area,        for example an active charcoal or a zeolite.

The manufacture of plaster panels, in particular a plasterboard, isknown per se.

Although the invention is more particularly described with regard toplaster panels, it is not limited to this type of material and includesplaster-based materials in any form whatsoever (powder, rendering,mortar, mastic, tile).

The plasterboard is formed via a continuous process which consists inmixing powdered calcined gypsum (calcium sulfate hemihydrate) with waterto form a paste which is continuously deposited between two sheets ofpaper. The product formed is pressed to obtain the desired thickness,and it is then transported continuously on a conveyor over a distanceallowing the paste to achieve a level of hardening sufficient to be ableto cut into boards of given length. The boards are then dried in an ovenso as to remove the excess water.

Conventionally, the powder components of the paste comprise calciumsulfate hemihydrate (CaSO₄.0.5 H₂O; calcined gypsum) and the optionaladditives described above. The calcined gypsum undergoes a hydrationreaction in the presence of water and becomes transformed into calciumsulfate dihydrate (CaSO₄.2 H₂O:gypsum).

The amount of calcined gypsum used to form the paste varies according tothe nature of the panel to be manufactured, generally from 40 to 150parts by weight per 100 parts by weight of water, preferably from 60 to120 parts.

The thickness of the board may vary within a wide range, for examplefrom 6 to 25 mm.

The metal complex of EDTA may be introduced into the plasterboard invarious ways.

According to a first preferred embodiment, the metal complex of EDTA isadded to the calcined gypsum paste before it is deposited between thesheets of paper.

The addition of metal complex of EDTA may take place during themanufacture of paste, for example by simultaneously or successivelyintroducing the calcined gypsum and the abovementioned compounds intowater, or after the paste has been obtained. The simultaneous additionof the constituents is advantageous since it is easier to perform.

This embodiment affords uniform distribution of the metal complex ofEDTA in the paste. According to a second embodiment, a layer of lowthickness, generally less than 2 mm and preferably less than 1 mm, of acalcined gypsum paste containing the metal complex of EDTA is depositedon the first sheets of paper (lower), followed by the calcined gypsumpaste, and finally the second sheets of paper (upper). The applicationof the paste containing the metal complex of EDTA may take place via anymeans known to those skilled in the art, for example via the rollercoating technique. This manner of proceeding makes it possible to applythe metal complex of EDTA to one face of the plasterboard and to only apart of the thickness.

According to a third embodiment, the metal complex of EDTA is added intoor onto the sheet(s) of paper serving as coating. The addition may takeplace during the manufacture of the paper, for example in the suspensionof cellulose fibres, or on at least one face of the sheet of paper, forexample by spraying.

The plaster-based material in accordance with the present invention maybe in the form of a powder (plaster, rendering, mortar), a paste(mastic, pointing material), a tile or a plaster panel. As moreparticularly regards the plaster panel, it may be a bare board or aboard coated on at least one of its faces with a sheet of paper, anacoustic panel comprising perforations, a panel of plaster and mineralwool or wood, or a board reinforced with fibres or a fabric.

The plaster-based material in accordance with the invention may be usedon walls, ceilings and floors, especially for coating or pointingplaster or cement panels or, as regards panels, for forming facings,partitions and suspended ceilings.

The use of the plaster-based material inside a building on a place ofdwelling, public place or workplace makes it possible to reduce theamount of volatile organic compounds present in the atmosphere, which isconsequently found to be made healthier.

The examples that follow illustrate the invention without, however,limiting it.

EXAMPLE 1

a) Manufacture of the Plaster-Based Material

995 g of calcium sulfate hemihydrate, 5.2 g of starch, 0.1 g of groundgypsum, 1.2 g of zinc-EDTA complex (sold by the company Synthron) and850 g of water are placed in a mixer.

The mixture is stirred for 60 seconds in order to obtain a paste.

The paste is poured into a grass mould (250 mm×200 mm) lined on itsinner face with a sheet of paper, and a second sheet of paper cut to thesizes of the mould is then applied on the paste.

After setting to a solid, the plasterboard is removed from the mould. Itis then dried in an oven whose atmosphere is saturated with water, underthe following conditions: at 180° C. until 80% of the water is removed,at 100° C. until 95% of the water is removed and at 40° C. for 24 hours.

The board is wrapped in an airtight bag that is resistant to ultravioletrays.

For comparative purposes, a board not containing any zinc-EDTA complex(comparative example) was prepared under the same conditions.

b) Capacity for Trapping Volatile Organic Compounds

The measurement of the capacity for trapping volatile organic compounds(acetaldehyde, acetone and benzene) is performed in a gastight testchamber.

The plasterboard (100 mm×20 mm; 125 g) is placed in the test chamber,and chamber is then hermetically closed. A continuous stream of air(relative humidity: 50%) containing 20 ppb of the volatile organiccompound to be tested is circulated in the chamber at a rate of 250ml/min.

The measurement of the amount of volatile organic compound is performedin real-time using an FTICR (Fourier transform ion cyclotron resonance)mass spectrometer equipped with a 1 Tesla magnet. The measurementprinciple is as follows: a semi-porous flat membrane made ofpolydimethylsiloxane (PDMS) acting as a barrier between the pressure atthe chamber outlet (atmospheric pressure) and the vacuum of the massspectrometer is used. The pressure difference on either side of themembrane and the semi-porous nature of the membrane are such that thevolatile organic compounds migrate more rapidly across the membrane thanthe other molecules contained in the injected air (oxygen, nitrogen,argon, carbon dioxide and water). This results in and enrichment involatile organic compounds and hence greater sensitivity of detection bythe mass spectrometer.

The results given in the table below correspond to a mean valueestablished on a series of three samples of the same plasterboard. Thetable indicates the percentage reduction in the content of volatileorganic compounds below:

Benzene Xylene Cyclohexanone (%) (%) (%) Ex. 1 52 52 70 Comparative Ex.0 0 0

The invention claimed is:
 1. A plaster-based building material,comprising a zinc complex of EDTA, wherein the zinc complex of EDTA isincluded in an amount selected to reduce an amount of ambient volatileorganic compounds in an environment in which the building material isused.
 2. The plaster-based building material according to claim 1,wherein a total amount of the zinc complex of EDTA ranges from 0.0001 to40 parts by weight per 100 parts by weight of plaster.
 3. Theplaster-based building material according to claim 1, further comprisingthe following additives in the following weight proportions, expressedper 100 parts by weight of plaster: 0.1 to 15 parts of an adhesionagent, 0.001 to 10 parts of a setting accelerator, 0 to 10 parts of abiocide, 0.0001 to 1 part of a foaming agent, 0 to 10 parts of at leastone water repellent, 0 to 20 parts of at least one fire retardant, 0 to20 parts of at least one reinforcer, 0 to 20 parts of an agent adaptedto trap formaldehyde, 0 to 20 parts of active charcoal or a zeolite. 4.The plaster-based building material according to claim 1, wherein theplaster-based material is in the form of a powder, a paste or a plasterpanel.
 5. The plaster-based building material according to claim 4,wherein the plaster-based material is a plasterboard.
 6. Theplaster-based building material according to claim 2, wherein the totalamount of the metal complex of EDTA ranges from 0.001 to 10 parts byweight per 100 parts by weight of plaster.
 7. The plaster-based buildingmaterial according to claim 6, wherein the total amount of the metalcomplex of EDTA ranges from 0.05 to 5 parts by weight per 100 parts byweight of plaster.
 8. The plaster-based building material according toclaim 3, wherein the adhesion agent is a starch, a dextrin or avegetable flour.
 9. The plaster-based building material according toclaim 3, wherein the setting accelerator is hydrated calcium sulfate orpotassium sulfate.
 10. The plaster-based building material according toclaim 3, wherein the biocide is sodium omadine.
 11. The plaster-basedbuilding material according to claim 3, wherein the foaming agent issodium lauryl sulfate.
 12. The plaster-based building material accordingto claim 3, wherein the at least one water repellent is a siloxane or apolysiloxane.
 13. The plaster-based building material according to claim3, wherein the at least one fire retardant is vermiculite, silica, aclay or metal fibres.
 14. The plaster-based building material accordingto claim 3, wherein the at least one reinforcer is polymer fibres,mineral fibres, animal or vegetable fibres.
 15. The plaster-basedbuilding material according to claim 3, wherein the agent adapted totrap formaldehyde is acetoacetamide, adipic acid dihydrazide or aprotein.